function node_access($op, $node = NULL, $uid = NULL) {
  // Convert the node to an object if necessary:
  $node = array2object($node);

  // If the node is in a restricted format, disallow editing.
  if ($op == 'update' && !filter_access($node->format)) {
    return FALSE;
  }

  if (user_access('administer nodes')) {
    return TRUE;
  }

  if (!user_access('access content')) {
    return FALSE;
  }

  if ($op == 'create' && ($grants = node_invoke_nodeapi($node, 'create'))) {
    foreach ($grants as $grant) {
      if (!$grant) {
        return FALSE;
      }
    }
  }
  // Can't use node_invoke(), because the access hook takes the $op parameter
  // before the $node parameter.
  $access = module_invoke(node_get_module_name($node), 'access', $op, $node);
  if (!is_null($access)) {
    return $access;
  }

  // If the module did not override the access rights, use those set in the
  // node_access table.
  if ($node->nid && $node->status) {
    $sql = 'SELECT COUNT(*) FROM {node_access} WHERE (nid = 0 OR nid = %d) AND CONCAT(realm, gid) IN (';
    $grants = array();
    foreach (node_access_grants($op, $uid) as $realm => $gids) {
      foreach ($gids as $gid) {
        $grants[] = "'". $realm . $gid ."'";
      }
    }
    $sql .= implode(',', $grants) .') AND grant_'. $op .' = 1';
    $result = db_query($sql, $node->nid);
    return (db_result($result));
  }
  return FALSE;
}